I loved Iron Man 3, and the twist was one of my favorite parts. I can see why purists hate it, but Ben Kingsley is fucking hilarious as Trevor Slattery, so that helps a lot for me.
Sure, but most of it is still done in a way that you don't have to watch anything else, to follow a specific movie or show. My mom isn't interested in any of the D+ series, but she still came to see Dr. Strange in the Multiverse of Madness and followed it fine. You will definitely get more out of them if you see the related stuff, but you don't need to.
The thing that disappointed me about Dr. Strange the most was it felt like Loki was supposed to set up Dr. Strange and Loki, or the events of Loki weren't even mentioned at all. Maybe I was just expecting too much.